This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Atrial fibrillation (AF), the most common cardiac arrhythmia encountered in clinical cardiology, affects more than 3 million Americans and its prevalence increases with age to approximately 6% in people over 65 years of age. The impact of AF on morbidity and mortality is substantial, as are the socioeconomic consequences in relationship to hospital admissions, chronic disease management and disabilities. Despite recent advances in the management of this disease, control of heart rate and prevention of systemic embolization remains the mainstay of therapy for the majority of patients. One reason for the limited success in therapy for AF may in part, be due to poor understanding of the disorder's molecular pathophysiology. AF is usually associated with cardiac pathology, including hypertensive heart disease, cardiomyopathy, valvular disease or atherosclerotic cardiovascular disease. In some instances, especially in the young, the disease has no apparent cause and is called "lone" AF. Lone AF accounts for 2-16% of all cases and, within this group falls the familial forms of the disease for which a genetic basis is likely. The purpose of this study is to store for future use a sample of blood to look for genetic factors (DNA) that may cause or relate to atrial fibrillation or other conditions or illnesses.